Wireless communication device and wireless communication method

ABSTRACT

A tuner receives a received signal using one of a plurality of transmission formats that use at least one of either a first frequency or a second frequency band. A determination unit determines the transmission format being used in the received signal from among the plurality of transmission formats. In the determination unit, a pattern matching unit stores in advance a plurality of patterns respectively expressing a received waveform of a preamble in each of the plurality of transmission formats, conducts a pattern matching process between the received signal and the each of the plurality of patterns, and obtains a correlation value. A transmission mode determination unit determines the transmission format being used in the received signal on the basis of the correlation value.

BACKGROUND

1. Technical Field

The present disclosure relates to a wireless communication device and awireless communication method.

2. Description of the Related Art

Heretofore, indoor communication has been the main target of the effortsof the wireless LAN standard in IEEE 802.11. Additional physical layerstandards have followed, primarily with the aim of increasingtransmission capacity, such as 802.11b (up to 11 Mbps), 802.11a/11g (upto 54 Mbps), 802.11n (up to 600 Mbps), and 802.11ac (up to 6.9 Gbps).Meanwhile, as the development of smart meters for realizing smart gridsintensifies, demand is rising for low-rate, long-range outdoortransmission. Debate also continues over issues such as the allocationof usable frequencies for specified low-power wireless intended for suchapplications. Given this background, the formulation of a newcommunication standard using the sub-GHz band (the frequency bandslightly lower than 1 GHz) is now being investigated. Additionally, in2010, an IEEE 802.11 task group focused on developing a wireless LANstandard using the frequency band up to 1 GHz, TGah (802.11ah) was alsoformed. The specification framework for TGah (802.11ah) achieves a datarate of up to 100 kbps, and a maximum transmission range of 1 km.

In standards since IEEE 802.11a that use OFDM modulation schemes,including TGah (802.11ah), a preamble at the beginning of a packet isused to establish various synchronizations, and burst communication isconducted. The preamble is made up of a short training field (STF; alsocalled the short preamble) and a long training field (LTF; also calledthe long preamble). The STF is used for automatic gain control (AGC), orautomatic frequency control (AFC) to conduct rough adjustment. The LTFis used for AFC to conduct fine adjustment, or channel estimation. Also,after the preamble, there is placed SIGNAL information for controlling adata field (also designated “DATA”). The SIGNAL information ismultiplexed by BPSK modulation that is strong against interference.

In TGah (802.11ah), it is anticipated that the standard will require acompatible communication device to be equipped with a function forcommunicating using the 1 MHz and 2 MHz signal bands. Consequently, in acommunication network formed by communication devices conforming to802.11ah, the formation of a communication network using both 1 MHz and2 MHz as signal bands is anticipated. In other words, an environment ofcoexisting 1 MHz/2 MHz channels is anticipated.

Accordingly, when conducting communication based on 802.11ah, acommunication device may need to determine whether a communication peeris transmitting using 1 MHz or 2 MHz as the signal band.

Similarly to 802.11ah, IEEE 802.11n is another standard thatcommunicates by switching between multiple transmission modes within acommunication network conforming to the same communication standard.Japanese Unexamined Patent Application Publication No. 2010-109401discloses a method of efficiently determining the transmission mode(transmission format) in 802.11n.

SUMMARY

However, with the method in Japanese Unexamined Patent ApplicationPublication No. 2010-109401, the transmission mode (transmission format)is identified on the basis of the SIGNAL information that is obtainedlast in the receiving process. For this reason, in Japanese UnexaminedPatent Application Publication No. 2010-109401, there is a lengthyprocessing time to conduct the transmission mode determination process.Also, in Japanese Unexamined Patent Application Publication No.2010-109401, reattempting a receiving operation requires storing allreceived data, and thus high-capacity memory is required. Additionally,the method in Japanese Unexamined Patent Application Publication No.2010-109401 is a detection of the frame format in 802.11n, which cannotbe applied directly to the determination of the transmission mode in802.11ah.

Thus, a non-limiting exemplary embodiment of the present disclosureprovides a wireless communication device and a wireless communicationmethod able accurately detect the transmission mode and improvecommunication efficiency for communication based on IEEE 802.11ah.

A wireless communication device according to an embodiment of thepresent disclosure is provided with: a receiving unit that receives asignal using one of a plurality of transmission formats that use atleast one of a first frequency band and a second frequency band; and adetermination unit that determines a transmission format being used inthe received signal from among the plurality of transmission formats,the determination unit comprising a pattern matching unit that stores aplurality of patterns respectively expressing a received waveform of apreamble in each of the plurality of transmission format, conducts apattern matching between the received signal and each of the pluralityof patterns, and obtains a correlation value, and a mode determinationunit that determines the transmission format being used in the receivedsignal on the basis of the obtained correlation value.

A wireless communication device according to an embodiment of thepresent disclosure is provided with: a receiving unit that receives asignal using one of a plurality of transmission formats that use atleast one of a first frequency band and a second frequency band; and adetermination unit that determines a transmission format being used inthe received signal from among the plurality of transmission formats.The determination unit includes a first extraction unit that extracts afirst component of the first frequency band from the received signal, asecond extraction unit that extracts a second component of the secondfrequency band from the received signal, a pattern matching unit thatstores a plurality of patterns respectively expressing a receivedwaveform of a preamble in each of the plurality of transmission formats,conducts a first pattern matching between the first component of thereceived signal and a first pattern corresponding to a transmissionformat that uses the first frequency band, conducts a second patternmatching between the second component of the received signal and asecond pattern corresponding to a transmission format that uses thesecond frequency band, conducts a third pattern matching between thereceived signal and a pattern corresponding to a transmission formatthat uses the first frequency band and the second frequency band, andobtains a correlation value, and a mode determination unit thatdetermines a transmission format being used in the received signal onthe basis of the correlation value.

A wireless communication device according to an embodiment of thepresent disclosure is provided with: a receiving unit that receives asignal using one of a plurality of transmission formats that use atleast one of a first frequency band and a second frequency band; and adetermination unit that determines a transmission format being used inthe received signal from among the plurality of transmission formats.The determination unit comprises a first extraction unit that extracts afirst component of the first frequency band from the received signal, afirst power calculation unit that calculates a first power differencebetween the received signal and the first component, a second extractionunit that extracts a second component of the second frequency band fromthe received signal, a second power calculation unit that calculates asecond power difference between the received signal and the secondcomponent, and a mode determination unit that determines thetransmission format being used in the received signal based on amagnitude relationship between the first power difference and apredetermined value, and a magnitude relationship between the secondpower difference and the predetermined value.

A wireless communication device according to an embodiment of thepresent disclosure is provided with: a receiving unit that receives asignal using one of a plurality of transmission formats that use atleast one of a first frequency band and a second frequency band; and adetermination unit that determines a transmission format being used inthe received signal from among the plurality of transmission formats.The determination unit includes a first extraction unit that extracts afirst component of the first frequency band from the received signal, afirst frequency shift unit that shifts the frequency of the firstcomponent toward higher frequency by half the width of the firstfrequency band, a second extraction unit that extracts a secondcomponent of the second frequency band from the received signal, asecond frequency shift unit that shifts the frequency of the secondcomponent toward lower frequency by half the width of the secondfrequency band, a pattern matching unit that conducts a pattern matchingbetween the frequency-shifted first component and the frequency-shiftedsecond component, and obtains a correlation value, and a modedetermination unit that determines a transmission format being used inthe received signal on the basis of the correlation value.

A wireless communication device according to an embodiment of thepresent disclosure is provided with: a receiving unit that receives asignal that includes a short training field (STF) including a pluralityof symbols, the received signal using one of a plurality of transmissionformats that use at least one of a first frequency band and a secondfrequency band; and a determination unit that determines a transmissionformat being used in the received signal from among the plurality oftransmission formats. The number of symbols in the STF of a secondtransmission format is half the number of symbols in the STF of a firsttransmission format. The determination unit comprises a delay unit thatdelays the received signal by a first time corresponding to the numberof symbols in the STF of the second transmission format, and a modedetermination unit configured so that, when a correlation value is highbetween the pre-delay received signal and the delayed received signalduring a period from a time point after the first time elapses since thebeginning of the pre-delay received signal to a time point after a timecorresponding to half of the symbols elapses, the mode determinationunit determines that a transmission format using one of either the firstfrequency band or the second frequency band is being used, and when thecorrelation value is low, determines that a transmission format usingboth the first frequency band and the second frequency band is beingused.

A wireless communication device according to an embodiment of thepresent disclosure is provided with: a receiving unit that receives asignal that includes a long training field (LTF) in which pilot signalsare multiplexed and a signal field in which control signals modulated bya modulation scheme using the same phase as, or a phase existing in anorthogonal relationship with, the phase in which the pilot signal isplaced, are multiplexed, and the received signal using one of aplurality of transmission formats that use at least one of a firstfrequency band and a second frequency band; and a determination unitthat determines a transmission format being used in the received signalfrom among the plurality of transmission formats by using a plurality ofsymbols, including symbols constituting the LTF and symbols constitutingthe signal field. The determination unit includes a differentialcomputation unit that conducts a differential computation betweenneighboring symbols in the time domain on three symbols from a 2ndsymbol to a 4th symbol starting from the beginning of the LTF from amongthe plurality of symbols, a square computation unit that computes thesquare of the differential computation result, and a mode determinationunit that determines a transmission format being used in the receivedsignal on the basis of whether a value indicating the squared result isa positive value or a negative value on the real axis.

A wireless communication device according to an embodiment of thepresent disclosure is provided with: a receiving unit that receives asignal that includes a long training field (LTF) in which pilot signalsare multiplexed, the received signal using one of a plurality oftransmission formats that use at least one of a first frequency band anda second frequency band; and a determination unit that uses symbolsincluded in the LTF to determine a transmission format being used in thereceived signal from among the plurality of transmission formats. Thedetermination unit includes a complex division unit that calculates anestimated channel state value for each of the plurality of transmissionformats by complexly dividing a first symbol and a second symbolstarting from the beginning of the LTF by a pilot pattern correspondingto each of the plurality of transmission formats, a symbol filter thatfilters each estimated channel state value in the symbol direction, acarrier filter that filters, in the carrier direction, each estimatedchannel state value filtered in the symbol direction, a powercalculation unit that calculates a power value for each of the pluralityof transmission formats using the estimated channel state value filteredin the carrier direction, and a mode determination unit that determinesthat the transmission format with the greatest power value is being usedin the received signal.

These general and specific aspects may be implemented using a system, amethod, and a computer program, and any combination of systems, methods,and computer programs.

According to the present disclosure, it is possible to accurately detectthe transmission mode and improve communication efficiency forcommunication based on IEEE 802.11ah. Additional benefits and advantagesof the disclosed embodiments will be apparent from the specification andFigures. The benefits and/or advantages may be individually provided bythe various embodiments and features of the specification and Figures,and need not all be provided in order to obtain one or more of the same.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating transmission formats of the 1 MHz/2 MHzbands in 802.11ah;

FIG. 2 is a diagram illustrating an example of subcarrier arrangement inthe 1 MHz/2 MHz signal spectra;

FIG. 3 is a block diagram illustrating a configuration of a wirelesscommunication device according to Embodiment 1 of the presentdisclosure;

FIGS. 4A to 4D are diagrams illustrating examples of 1 MHz/2 MHz signalspectra in the case of setting the signal receiving band to 2 MHz;

FIG. 5 is a block diagram illustrating an internal configuration of adetermination unit according to Embodiment 1 of the present disclosure;

FIG. 6 is a diagram illustrating an example of received waveformpatterns of preambles according to Embodiment 1 of the presentdisclosure;

FIG. 7 is a block diagram illustrating an internal configuration of adetermination unit according to Embodiment 2 of the present disclosure;

FIGS. 8A to 8D are diagrams illustrating a band restriction processaccording to Embodiment 2 of the present disclosure;

FIG. 9 is a block diagram illustrating an internal configuration of adetermination unit according to Embodiment 3 of the present disclosure;

FIGS. 10A to 10C are diagrams illustrating a band restriction processaccording to Embodiment 3 of the present disclosure (for the case ofplacement mode 1L);

FIGS. 11A to 11C are diagrams illustrating a band restriction processaccording to Embodiment 3 of the present disclosure (for the case ofplacement mode 1U);

FIGS. 12A to 12C are diagrams illustrating a band restriction processaccording to Embodiment 3 of the present disclosure (for the case ofplacement mode 1D);

FIGS. 13A to 13C are diagrams illustrating a band restriction processaccording to Embodiment 3 of the present disclosure (for the case ofplacement mode 2C);

FIG. 14 is a diagram illustrating correspondence relationships betweensignal power difference and transmission mode according to Embodiment 3of the present disclosure;

FIG. 15 is a block diagram illustrating an internal configuration of adetermination unit according to Embodiment 4 of the present disclosure;

FIG. 16A is a diagram illustrating a signal spectrum of placement mode1D;

FIGS. 16B to 16E are diagrams illustrating a band restriction andfrequency shift process according to Embodiment 4 of the presentdisclosure (for the case of placement mode 1D);

FIG. 17A is a diagram illustrating a signal spectrum of placement mode2C;

FIGS. 17B to 17E are diagrams illustrating a band restriction andfrequency shift process according to Embodiment 4 of the presentdisclosure (for the case of placement mode 2C);

FIG. 18 is a diagram illustrating correspondence relationships betweencorrelation value and transmission mode according to Embodiment 4 of thepresent disclosure;

FIG. 19 is a block diagram illustrating an internal configuration of adetermination unit according to Embodiment 5 of the present disclosure;

FIG. 20 is a diagram illustrating a delay process for signals in eachtransmission format according to Embodiment 5 of the present disclosure;

FIG. 21 is a block diagram illustrating a configuration of a wirelesscommunication device according to Embodiment 6 of the presentdisclosure;

FIG. 22 is a block diagram illustrating an internal configuration of adetermination unit according to Embodiment 6 of the present disclosure;

FIG. 23 is a diagram illustrating the relative position of eachtransmission format aligned at the beginning of the LTF according toEmbodiment 6 of the present disclosure;

FIG. 24 is a diagram accompanying explanation of a transmission modedetermination process according to Embodiment 6 of the presentdisclosure (for the case of 1 MHz format);

FIG. 25 is a diagram accompanying explanation of a transmission modedetermination process according to Embodiment 6 of the presentdisclosure (for the case of 2 MHz short format);

FIG. 26 is a diagram accompanying explanation of a transmission modedetermination process according to Embodiment 6 of the presentdisclosure (for the case of 2 MHz long format);

FIG. 27 is a flowchart illustrating the flow of a transmission modedetermination process according to Embodiment 6 of the presentdisclosure;

FIG. 28 is a flowchart illustrating the flow of a transmission modedetermination process according to Embodiment 6 of the presentdisclosure;

FIG. 29 is a block diagram illustrating an internal configuration of adetermination unit according to Embodiment 7 of the present disclosure;and

FIGS. 30A and 30B are diagrams illustrating examples ofcross-correlation values in the STF according to Embodiment 8 of thepresent disclosure.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of the present disclosure will bedescribed in detail and with reference to the drawings.

[Transmission Format]

FIG. 1 illustrates transmission formats (signal transmission modes) usedin 802.11ah. In FIG. 1, the horizontal axis represents the time domain,while the vertical axis represents the frequency domain.

Transmission formats are roughly divided into four types. Specifically,these types are the 1 MHz format, the 1 MHz Duplicate format (alsocalled Duplicate mode), the 2 MHz short format, and the 2 MHz longformat.

Specifically, the 1 MHz format uses the 1 MHz bandwidth, and is made upof the STF, LTF1, SIG, LTF2 to LTFN, and DATA.

The 1 MHz Duplicate format uses the 2 MHz band to multiplex two of thesame 1 MHz frame packets.

The 2 MHz short format uses the 2 MHz bandwidth. The 2 MHz short formatis made up of the STF, LTF1, SIG, LTF2 to LTFN, and DATA.

The 2 MHz long format uses the 2 MHz bandwidth. The 2 MHz long format ismade up of the STF, LTF1, SIG-A, D-STF, D-LTF1 to D-LTFN, SIG-B, andDATA.

Also, as illustrated in FIG. 1, each transmission format is made up of atime-division multiplexed preamble (STF and LTF), signal field (SIG),and data field (DATA). In the signal field (SIG), control informationfor the data field (SIGNAL information) is multiplexed. In the datafield (DATA), the data (payload) is multiplexed.

In the STF at the beginning, a fixed pattern of short training symbols(STS) with a period of T_(S) are repeatedly placed 20 times in the 1 MHzformat, and 10 times in the 2 MHz format. In other words, the number ofSTS in the 2 MHz format is half the number of STS in the 1 MHz format.The STF is used for AGC, rough AFC, or packet detection.

In the LTF following the STF, a fixed pattern of long training symbols(LTS) with a period of T_(L) are repeatedly placed four times in the 1MHz format, and two times in the 2 MHz format. In other words, thenumber of LTS in the 2 MHz format is half the number of LTS in the 1 MHzformat. Also, a guard interval of a long preamble portion is added atthe beginning of the LTF or among the LTS.

After the LTF, the signal field (SIG) that transmits information fordemodulating the payload portion (such as the modulation scheme) isplaced, and after that, the payload (DATA) is placed.

Also, in 802.11ah, signals are modulated by OFDM. As illustrated in FIG.2, there are placed subcarriers mapped in the frequency domain usingphase-shift keying (PSK) or quadrature amplitude modulation (QAM).

Embodiment 1 Configuration of Wireless Communication Device 100

FIG. 3 is a block diagram illustrating a configuration of a wirelesscommunication device 100 according to the present embodiment. Thewireless communication device 100 is a communication device thatconducts communication conforming to 802.11ah, for example. FIG. 3illustrates a configuration of a circuit in the wireless communicationdevice 100 that conducts a receiving process in the physical layer.

The wireless communication device 100 illustrated in FIG. 3 includes atuner 101, a determination unit 102, a synchronization unit 103, a fastFourier transform (FFT) unit 104, an equalization unit 105, and an errorcorrection unit 106.

The tuner 101 conducts channel selection to synchronize with thefrequency band being used for wireless communication. During the channelselection process, when it is unknown whether the peer communicationdevice communicating with the wireless communication device 100 istransmitting signals using 1 MHz or 2 MHz, the tuner 101 sets thereceive band to 2 MHz and conducts the receiving process.

FIGS. 4A to 4D illustrate the spectral placement of signals (OFDMsignals) conforming to 802.11ah in received signals received by thetuner 101. As illustrated in FIGS. 4A to 4D, in 802.11ah, four types ofspectral placement modes are envisioned. Specifically, FIG. 4Aillustrates a case in which an OFDM signal 11 is placed in the 1 MHzband on the low-frequency side (hereinafter also called the lower band)included in the 2 MHz band (hereinafter, this placement is alsodesignated “1L”). FIG. 4B illustrates a case in which an OFDM signal 12is placed in the 1 MHz band on the high-frequency side (hereinafter alsocalled the higher band) included in the 2 MHz band (hereinafter, thisplacement is also designated “1U”). FIG. 4C illustrates the case ofDuplicate mode, in which the OFDM signal 11 is placed in the lower 1 MHzband within the 2 MHz band, and an OFDM signal 12 identical to the OFDMsignal 11 is placed in the higher 1 MHz band (hereinafter, thisplacement is also designated “1D”). FIG. 4D illustrates a case in whicha 2 MHz band OFDM signal 13 is placed in the 2 MHz band (hereinafter,this placement is also designated “2C”). In other words, FIGS. 4A and 4Bcorrespond to the 1 MHz format that uses either one of two bands, whileFIG. 4C corresponds to the 1 MHz Duplicate format that uses two bands,and FIG. 4D corresponds to the 2 MHz (short/long) format that uses twobands. A received signal is transmitted using any one of the abovetransmission formats.

The determination unit 102 determines the transmission mode(transmission format) of the received signal by using the intervalcorresponding to the preamble (STF, LTF) in a received signal receivedfrom the tuner 101. Note that a detailed description of the transmissionmode determination process by the determination unit 102 will be givenlater.

The synchronization unit 103, the FFT unit 104, the equalization unit105, and the error correction unit 106 conduct the following variousprocesses in accordance with the transmission mode (transmission format)determined by the determination unit 102.

The synchronization unit 103 detects the timings at which to conduct anFFT process by using the preamble in the 802.11ah frame inside thereceived signal received from the tuner 101.

The FFT unit 104 conducts an FFT process on the received signal at thetimings detected by the synchronization unit 103.

The equalization unit 105 conducts an equalization process on theFFT-processed signal.

The error correction unit 106 conducts an error correction process onthe equalized signal.

[Operation of Determination Unit 102]

Next, a transmission mode determination method used by the determinationunit 102 of the wireless communication device 100 illustrated in FIG. 3will be described in detail.

FIG. 5 is a block diagram illustrating an internal configuration of thedetermination unit 102.

The determination unit 102 illustrated in FIG. 5 includes patternmatching units 201-1 to 201-4, and a transmission mode determinationunit 202.

The pattern matching units 201-1 to 201-4 respectively correspond to thefour types of spectral placement modes (1L, 1U, 1D, 2C) illustrated inFIG. 4. The pattern matching units 201-1 to 201-4 store patterns(preamble patterns 1 to 4) in advance that express the received waveformof the preamble (STF, LTF) in a corresponding spectral placement mode.The pattern matching units 201-1 to 201-4 conduct a pattern-matchingprocess on the received signal received from the tuner 101 and thestored preamble patterns, and output pattern matching results(correlation values) to the transmission mode determination unit 202.

The transmission mode determination unit 202 uses the pattern matchingresults received from each of the pattern matching units 201-1 to 201-4to determine the spectral placement mode being used in the receivedsignal. In other words, the transmission mode determination unit 202determines that the transmission format (spectral placement mode)corresponding to the preamble pattern having the highest correlationwith the received signal is being used in the received signal. Thetransmission mode determination unit 202 outputs the transmission mode(placement mode) resulting from the determination to each of thesynchronization unit 103, the FFT unit 104, the equalization unit 105,and the error correction unit 106.

FIG. 6 illustrates an example of received signal waveforms of thepreambles (STF and LTF) corresponding to each of the spectral placementmodes illustrated in FIGS. 4A to 4D.

As illustrated in FIG. 6, differences occur in the preamble patternsdepending on the spectral placement mode. This means that even thoughthe transmitting side transmits the same signal as the preamble, thepattern of the preamble on the receiving side differs according to thespectral placement illustrated in FIGS. 4A to 4D.

In other words, in the determination unit 102, the transmission mode maybe determined by identifying which of the mutually different preamblepatterns matches the waveform of the preamble in the received signal.

In so doing, in the wireless communication device 100, it is possible toidentify the transmission mode before conducting the various receivingprocesses (the processes of the synchronization unit 103, the FFT unit104, the equalization unit 105, and the error correction unit 106).Consequently, according to the present embodiment, a lengthy processingtime for conducting the transmission mode determination process may beavoided.

Furthermore, according to the present embodiment, since the transmissionmode is determined before conducting receiving processes, it is notnecessary to store all received data in the case of reattempting areceiving operation as in Japanese Unexamined Patent ApplicationPublication No. 2010-109401, and thus high-capacity memory is notrequired.

Consequently, according to the present embodiment, it is possible toaccurately detect the transmission mode and improve communicationefficiency for communication based on IEEE 802.11ah.

Embodiment 2

In the present embodiment, the operation of the determination unit ofthe wireless communication device 100 (FIG. 3) differs compared toEmbodiment 1.

FIG. 7 is a block diagram illustrating an internal configuration of adetermination unit 102 a according to the present embodiment. Note thatin FIG. 7, the same signs are given to components that conduct the sameprocesses as Embodiment 1 (FIG. 5), and description thereof will bereduced or omitted.

In the determination unit 102 a illustrated in FIG. 7, a lowerextraction unit 301 extracts the lower 1 MHz signal from the receivedsignal in the 2 MHz band by applying a band limit that allows thecomponent of the lower 1 MHz band to pass through. The lower extractionunit 301 outputs the extracted signal to the pattern matching unit201-1.

A higher extraction unit 302 extracts the higher 1 MHz signal from thereceived signal in the 2 MHz band by applying a band limit that allowsthe component of the higher 1 MHz band to pass through. The higherextraction unit 302 outputs the extracted signal to the pattern matchingunit 201-2.

In the present embodiment, the pattern matching unit 201-1 correspondsto the spectral placement mode 1L (see FIG. 4A), while the patternmatching unit 201-2 corresponds to the spectral placement mode 1U (seeFIG. 4B). Also, the pattern matching units 201-3 and 201-4 respectivelycorrespond to either of the spectral placement modes 1D and 2C.

Similarly to Embodiment 1, the pattern matching units 201-1 to 201-4conduct a pattern matching process on the input signal. In other words,the pattern matching unit 201-1 conducts a pattern matching process onthe signal of the lower 1 MHz band and a preamble pattern correspondingto the placement mode 1L. Also, the pattern matching unit 201-2 conductsa pattern matching process on the signal of the higher 1 MHz band and apreamble pattern corresponding to the placement mode 1U.

FIGS. 8A to 8D are diagrams illustrating operation of the lowerextraction unit 301 and the higher extraction unit 302 according to thepresent embodiment.

FIG. 8A illustrates the frequency spectrum of the received signal in thecase of using the spectral placement mode 1L. In FIG. 8A, the desiredOFDM signal 11 is included in the lower 1 MHz band (signal band), whilea noise component 21 is included in the higher 1 MHz band.

Meanwhile, as illustrated in FIG. 8B, the lower extraction unit 301applies a band limit 51 that allows the lower 1 MHz band to passthrough. Consequently, as illustrated in FIG. 8B, the OFDM signal 11 inthe lower 1 MHz signal band passes through as-is, whereas in the higher1 MHz band, the noise component 21 is suppressed to become a noisecomponent 22.

Thus, the pattern matching unit 201-1 is able to conduct a patternmatching process on a received signal in which band components otherthan the anticipated signal band (1L) are suppressed, and the preamblepattern of the placement mode 1L. As a result, the accuracy of patternmatching related to the placement mode 1L by the pattern matching unit201-1 may be improved.

Similarly, FIG. 8C illustrates the frequency spectrum of the receivedsignal in the case of using the spectral placement mode 1U. In FIG. 8C,the desired OFDM signal 12 is included in the higher 1 MHz band (signalband), while a noise component 23 is included in the lower 1 MHz band.

Meanwhile, as illustrated in FIG. 8D, the higher extraction unit 302applies a band limit 52 that allows the higher 1 MHz band to passthrough. Consequently, as illustrated in FIG. 8D, the OFDM signal 12 inthe higher 1 MHz signal band passes through as-is, whereas in the lower1 MHz band, the noise component 23 is suppressed to become a noisecomponent 24.

Thus, the pattern matching unit 201-2 is able to conduct a patternmatching process on a received signal in which band components otherthan the anticipated signal band (1U) are suppressed, and the preamblepattern of the placement mode 1U. As a result, the accuracy of patternmatching related to the placement mode 1U by the pattern matching unit201-2 may be improved.

As above, according to the present embodiment, it is possible toaccurately detect the transmission mode and improve communicationefficiency for communication based on IEEE 802.11ah, similarly toEmbodiment 1. In addition, according to the present embodiment, thedetermination unit 102 a is able to accurately conduct a patternmatching process even though a noise component is included in thereceived signal. Consequently, the transmission mode (placement mode)determination accuracy may be further improved compared to Embodiment 1.

Embodiment 3

In the present embodiment, the operation of the determination unit ofthe wireless communication device 100 (FIG. 3) differs compared toEmbodiment 1 or 2.

FIG. 9 is a block diagram illustrating an internal configuration of adetermination unit 102 b according to the present embodiment. Note thatin FIG. 9, the same signs are given to components that conduct the sameprocesses as Embodiment 2 (FIG. 7), and description thereof will bereduced or omitted.

In the determination unit 102 b illustrated in FIG. 9, a signal powerdifference calculating unit 401 calculates the signal power differencebetween the received signal received from the lower extraction unit 301(the band-limited (lower 1 MHz band) signal), and the received signalreceived from the tuner 101 (the 2 MHz band signal before bandlimiting).

A signal power difference calculating unit 402 calculates the signalpower difference between the received signal received from the higherextraction unit 302 (the band-limited (higher 1 MHz band) signal), andthe received signal received from the tuner 101 (the 2 MHz band signalbefore band limiting).

A transmission mode determination unit 403 makes a determination of thetransmission mode (spectral placement mode) being used in the receivedsignal on the basis of the combination of the signal power differencereceived from the signal power difference calculating unit 401 and thesignal power difference received from the signal power differencecalculating unit 402. In other words, the transmission modedetermination unit 403 determines the transmission mode being used inthe received signal on the basis of a magnitude relationship between thesignal power difference received from the signal power differencecalculating unit 401 and a threshold value, and a magnitude relationshipbetween the signal power difference received from the signal powerdifference calculating unit 402 and a threshold value.

Hereinafter, operation of the transmission mode determination process bythe determination unit 102 b will be described in detail.

<Spectral Placement Mode 1L>

FIGS. 10A to 10C illustrate how the frequency spectrum changes in thedetermination unit 102 b in the case of receiving a signal in thespectral placement mode 1L.

FIG. 10A illustrates the signal spectrum of a signal in the spectralplacement mode 1L (the signal before band limiting).

FIG. 10B illustrates the signal spectrum after the lower extraction unit301 applies the band limit 51 (band-limited signal). As illustrated inFIG. 10B, since the OFDM signal 11 is placed in the lower 1 MHz band (inthe passband of the band limit 51), the signal component passes throughwithout being suppressed. In this way, since the signal component isnearly the same before and after the band limiting, in the signal powerdifference calculating unit 401, the power difference between thesignals before and after band limiting (FIGS. 10A and 10B) is small.

FIG. 10C illustrates the signal spectrum after the higher extractionunit 302 applies the band limit 52 (band-limited signal). As illustratedin FIG. 10C, since the OFDM signal 11 is placed in the lower 1 MHz band(outside the passband of the band limit 52), the signal component issuppressed to become a signal 11 a. In this way, since the signal powerof the signal component decreases after the band limiting, in the signalpower difference calculating unit 402, the power difference between thesignals before and after band limiting (FIGS. 10A and 10C) is large.

<Spectral Placement Mode 1U>

FIGS. 11A to 11C illustrate how the frequency spectrum changes in thedetermination unit 102 b in the case of receiving a signal in thespectral placement mode 1U.

FIG. 11A illustrates the signal spectrum of a signal in the spectralplacement mode 1U (the signal before band limiting).

FIG. 11B illustrates the signal spectrum after the lower extraction unit301 applies the band limit 51 (band-limited signal). As illustrated inFIG. 11B, since the OFDM signal 12 is placed in the higher 1 MHz band(outside the passband of the band limit 51), the signal component issuppressed to become a signal 12 a. In this way, since the signal powerof the signal component decreases after the band limiting, in the signalpower difference calculating unit 401, the power difference between thesignals before and after band limiting (FIGS. 11A and 11B) is large.

FIG. 11C illustrates the signal spectrum after the higher extractionunit 302 applies the band limit 52 (band-limited signal). As illustratedin FIG. 11C, since the OFDM signal 12 is placed in the higher 1 MHz band(in the passband of the band limit 52), the signal component passesthrough without being suppressed. In this way, since the signalcomponent is nearly the same before and after the band limiting, in thesignal power difference calculating unit 402, the power differencebetween the signals before and after band limiting (FIGS. 11A and 11C)is small.

<Spectral Placement Mode 1D>

FIGS. 12A to 12C illustrate how the frequency spectrum changes in thedetermination unit 102 b in the case of receiving a signal in thespectral placement mode 1D.

FIG. 12A illustrates the signal spectrum of a signal in the spectralplacement mode 1D (the signal before band limiting).

FIG. 12B illustrates the signal spectrum after the lower extraction unit301 applies the band limit 51 (band-limited signal). As illustrated inFIG. 12B, since the OFDM signal 11 placed in the lower 1 MHz band isplaced in the passband of the band limit 51, the signal component passesthrough without being suppressed. On the other hand, since the OFDMsignal 12 placed in the higher 1 MHz band is placed outside the passbandof the band limit 51, the signal component is suppressed to become asignal 12 b. In this way, since the signal power of the signal componentin the higher 1 MHz band decreases after the band limiting, in thesignal power difference calculating unit 401, the power differencebetween the signals before and after band limiting (FIGS. 12A and 12B)is large.

FIG. 12C illustrates the signal spectrum after the higher extractionunit 302 applies the band limit 52 (band-limited signal). As illustratedin FIG. 12C, since the OFDM signal 11 placed in the lower 1 MHz band isplaced outside the passband of the band limit 52, the signal componentis suppressed to become a signal 11 b. On the other hand, since the OFDMsignal 12 placed in the higher 1 MHz band is placed in the passband ofthe band limit 52, the signal component passes through without beingsuppressed. In this way, since the signal power of the signal componentin the lower 1 MHz band decreases after the band limiting, in the signalpower difference calculating unit 402, the power difference between thesignals before and after band limiting (FIGS. 12A and 12C) is large.

<Spectral Placement Mode 2C>

FIGS. 13A to 13C illustrate how the frequency spectrum changes in thedetermination unit 102 b in the case of receiving a signal in thespectral placement mode 2C.

FIG. 13A illustrates the signal spectrum of a signal in the spectralplacement mode 2C (the signal before band limiting).

FIG. 13B illustrates the signal spectrum after the lower extraction unit301 applies the band limit 51 (band-limited signal). As illustrated inFIG. 13B, since the signal component 13 a of the OFDM signal 13 placedin the lower 1 MHz band is placed in the passband of the band limit 51,the signal component passes through without being suppressed. On theother hand, since the signal component 13 b of the OFDM signal 13 placedin the higher 1 MHz band is placed outside the passband of the bandlimit 51, the signal component is suppressed. In this way, since thesignal power of the signal component 13 b in the higher 1 MHz banddecreases after the band limiting, in the signal power differencecalculating unit 401, the power difference between the signals beforeand after band limiting (FIGS. 13A and 13B) is large.

FIG. 13C illustrates the signal spectrum after the higher extractionunit 302 applies the band limit 52 (band-limited signal). As illustratedin FIG. 13C, since the signal component 13 d of the OFDM signal 13placed in the lower 1 MHz band is placed outside the passband of theband limit 52, the signal component is suppressed. On the other hand,since the signal component 13 c of the OFDM signal 13 placed in thehigher 1 MHz band is placed in the passband of the band limit 52, thesignal component passes through without being suppressed. In this way,since the signal power of the signal component 13 d in the lower 1 MHzband decreases after the band limiting, in the signal power differencecalculating unit 402, the power difference between the signals beforeand after band limiting (FIGS. 13A and 13C) is large.

The correspondence relationships illustrated in FIG. 14 summarize thecombinations of signal power differences before and after band limitingin the higher 1 MHz band and the lower 1 MHz band for each of thereceived signals in the spectral placement modes 1L, 1U, 1D, and 1Cdescribed above. For example, in FIG. 14, “small” indicates that thesignal power difference is less than a threshold value, while “large”indicates that the signal power difference is equal to or greater than athreshold value.

The transmission mode determination unit 403 determines the transmissionmode (spectral placement mode) of the received signal on the basis ofthe combination of the signal power differences received from the signalpower difference calculating units 401 and 402, that is, on the basis ofthe correspondence relationships illustrated in FIG. 14.

For example, when the signal power difference of the lower 1 MHz acrossthe band limit 51 is “small”, and the signal power difference of thehigher 1 MHz band across the band limit 52 is “large”, the transmissionmode determination unit 403 determines that the transmission formatusing the higher 1 MHz band (1U) is being used. Similarly, when thesignal power difference of the lower 1 MHz across the band limit 51 is“large”, and the signal power difference of the higher 1 MHz band acrossthe band limit 52 is “small”, the transmission mode determination unit403 determines that the transmission format using the lower 1 MHz band(1L) is being used.

Also, when the signal power difference of the lower 1 MHz across theband limit 51 is “large”, and the signal power difference of the higher1 MHz band across the band limit 52 is “large”, the transmission modedetermination unit 403 determines that a transmission format using the 2MHz band (1D or 2C) is being used.

In other words, as illustrated in FIG. 14, the transmission modedetermination unit 403 is able to determine the transmission mode whiledistinguishing between the transmission formats (spectral placementmodes) 1U, 1L, and 1D or 2C. In other words, the transmission modedetermination unit 403 is able to determine the bandwidth of thereceived signal (1 MHz or 2 MHz), and the band in which a 1 MHz bandreceived signal is placed (higher 1 MHz or lower 1 MHz).

As above, according to the present embodiment, the determination unit102 b is able to use signal power differences before and after bandlimiting to accurately detect the transmission mode (placement mode),and improve communication efficiency.

For example, by applying the transmission mode determination methodaccording to the present embodiment, a terminal device that supports 1MHz formats (1U and 1L) is able to accurately determine the twotransmission modes.

Embodiment 4

In the present embodiment, the operation of the determination unit ofthe wireless communication device 100 (FIG. 3) differs compared toEmbodiments 1 to 3.

FIG. 15 is a block diagram illustrating an internal configuration of adetermination unit 102 c according to the present embodiment. Note thatin FIG. 15, the same signs are given to components that conduct the sameprocesses as Embodiment 2 (FIG. 7), and description thereof will bereduced or omitted.

In the determination unit 102 c illustrated in FIG. 15, a frequencyshift unit 501 shifts by +0.5 MHz the frequency of the signal receivedfrom the lower extraction unit 301 (the signal after the band limit thatpasses the lower 1 MHz band). In other words, the band-limited signal isfrequency-shifted toward higher frequency by half (0.5 MHz) of the lower1 MHz band.

A frequency shift unit 502 shifts by −0.5 MHz the frequency of thesignal received from the higher extraction unit 302 (the signal afterthe band limit that passes the higher 1 MHz band). In other words, theband-limited signal is frequency-shifted toward lower frequency by half(0.5 MHz) of the higher 1 MHz band.

A pattern matching unit 503 conducts a pattern matching process(correlation process) on the signal received from the frequency shiftunit 501 and the signal received from the frequency shift unit 502, andobtains a correlation value.

A transmission mode determination unit 504 uses the pattern matchingresult (correlation value) received from the pattern matching unit 503to determine the transmission mode (spectral placement mode) being usedin the received signal.

Hereinafter, operation of the transmission mode determination process bythe determination unit 102 c will be described in detail.

<Spectral Placement Mode 1D>

FIGS. 16A to 16E illustrate how the frequency spectrum changes in thedetermination unit 102 c in the case of receiving a signal in thespectral placement mode 1D.

FIG. 16A illustrates the signal spectrum of a signal in the spectralplacement mode 1D.

FIG. 16B illustrates the signal spectrum after the lower extraction unit301 applies the band limit 51. As illustrated in FIG. 16B, since theOFDM signal 11 placed in the lower 1 MHz band is placed in the passbandof the band limit 51, the signal component passes through without beingsuppressed. On the other hand, since the OFDM signal 12 placed in thehigher 1 MHz band is placed outside the passband of the band limit 51,the signal component is suppressed to become a signal 12 c. FIG. 16Cillustrates how the frequency shift unit 501 shifts the frequency of thesignal illustrated in FIG. 16B by +0.5 MHz. As illustrated in FIG. 16C,the signal in the lower 1 MHz band is frequency-shifted by +0.5 MHz tobecome a signal 11 c, while the signal in the higher 1 MHz band isfrequency-shifted by +0.5 MHz to become a signal 12 d. As a result, thesignal in the lower 1 MHz band illustrated in FIG. 16B becomes centeredon a frequency of 0 (MHz) in FIG. 16C.

FIG. 16D illustrates the signal spectrum after the higher extractionunit 302 applies the band limit 52. As illustrated in FIG. 16D, sincethe OFDM signal 11 placed in the lower 1 MHz band is placed outside thepassband of the band limit 52, the signal component is suppressed tobecome a signal 11 d. On the other hand, since the OFDM signal 12 placedin the higher 1 MHz band is placed in the passband of the band limit 52,the signal component passes through without being suppressed. FIG. 16Eillustrates how the frequency shift unit 502 shifts the frequency of thesignal illustrated in FIG. 16D by −0.5 MHz. As illustrated in FIG. 16E,the signal in the lower 1 MHz band is frequency-shifted by −0.5 MHz tobecome a signal 11 e, while the signal in the higher 1 MHz band isfrequency-shifted by −0.5 MHz to become a signal 12 e. As a result, thesignal in the higher 1 MHz band illustrated in FIG. 16D becomes centeredon a frequency of 0 (MHz) in FIG. 16E.

At this point, the signal 12 d illustrated in FIG. 16C and the signal 11e illustrated in FIG. 16E have very slight signal power due to the bandlimiting, and may be ignored in the receiving band. Also, the signal 11c illustrated in FIG. 16C and the signal 12 e illustrated in FIG. 16Eare placed at the same frequency as a result of the frequency shift. Inaddition, the signal 11 c illustrated in FIG. 16C and the signal 12 eillustrated in FIG. 16E are both signal components that passed throughthe band limit without being suppressed, correspond to the signals 11and 12 in FIG. 16A, respectively, and are the same as each other.

Consequently, the signal in the receiving band illustrated in FIG. 16Cand the signal in the receiving band illustrated in FIG. 16E have a highsimilarity (correlation).

In other words, the pattern matching unit 503 determines that thecorrelation is high according to the pattern matching process on thesignals respectively received from the frequency shift units 501 and502.

<Spectral Placement Mode 2C>

FIGS. 17A to 17E illustrate how the frequency spectrum changes in thedetermination unit 102 c in the case of receiving a signal in thespectral placement mode 2C.

FIG. 17A illustrates the signal spectrum of a signal in the spectralplacement mode 2C. As illustrated in FIG. 17A, the 2 MHz OFDM signal 13is made up of a signal component 14 placed in the higher 1 MHz band, anda signal component 15 placed in the lower 1 MHz band.

FIG. 17B illustrates the signal spectrum after the lower extraction unit301 applies the band limit 51. As illustrated in FIG. 17B, since thesignal component 15 placed in the lower 1 MHz band is placed in thepassband of the band limit 51, the signal component passes throughwithout being suppressed. On the other hand, since the signal component14 placed in the higher 1 MHz band is placed outside the passband of theband limit 51, the signal component is suppressed to become a signal 14a. FIG. 17C illustrates how the frequency shift unit 501 shifts thefrequency of the signal illustrated in FIG. 17B by +0.5 MHz. Asillustrated in FIG. 17C, the signal in the lower 1 MHz band isfrequency-shifted by +0.5 MHz to become a signal 15 a, while the signalin the higher 1 MHz band is frequency-shifted by +0.5 MHz to become asignal 14 b. As a result, the signal in the lower 1 MHz band illustratedin FIG. 17B becomes centered on a frequency of 0 (MHz) in FIG. 17C.

FIG. 17D illustrates the signal spectrum after the higher extractionunit 302 applies the band limit 52. As illustrated in FIG. 17D, sincethe signal component 15 placed in the lower 1 MHz band is placed outsidethe passband of the band limit 52, the signal component is suppressed tobecome a signal 15 b. On the other hand, since the signal component 14placed in the higher 1 MHz band is placed in the passband of the bandlimit 52, the signal component passes through without being suppressed.FIG. 17E illustrates how the frequency shift unit 502 shifts thefrequency of the signal illustrated in FIG. 17D by −0.5 MHz. Asillustrated in FIG. 17E, the signal in the lower 1 MHz band isfrequency-shifted by −0.5 MHz to become a signal 15 c, while the signalin the higher 1 MHz band is frequency-shifted by −0.5 MHz to become asignal 14 c. As a result, the signal in the lower 1 MHz band illustratedin FIG. 17D becomes centered on a frequency of 0 (MHz) in FIG. 17E.

At this point, the signal 14 b illustrated in FIG. 17C and the signal 15c illustrated in FIG. 17E have very slight signal power due to the bandlimiting, and may be ignored in the receiving band. Also, the signal 15a illustrated in FIG. 17C and the signal 14 c illustrated in FIG. 17Eare placed at nearly the same frequency as a result of the frequencyshift. However, the signal 15 a illustrated in FIG. 17C and the signal14 c illustrated in FIG. 17E are both signal components that passedthrough the band limit without being suppressed, correspond to thesignal components 15 and 14 in FIG. 17A, respectively, and are differentfrom each other.

Consequently, the signal in the receiving band illustrated in FIG. 17Cand the signal in the receiving band illustrated in FIG. 17E have a lowsimilarity (correlation).

In other words, the pattern matching unit 503 determines that thecorrelation is low according to the pattern matching process on thesignals respectively received from the frequency shift units 501 and502.

Note that for the spectral placement modes 1U and 1L, since a signalcomponent is placed in one of either the higher 1 MHz band or the lower1 MHz band, a low similarity (correlation) will be determined frompattern matching between the higher 1 MHz band the lower 1 MHz band forreceived signals obtained by the above operation.

The correspondence relationships illustrated in FIG. 18 summarize thepattern matching results (correlation) between the higher 1 MHz band andthe lower 1 MHz band for each of the received signals in the spectralplacement modes 1D and 2C described above. For example, in FIG. 18,“small” indicates that the correlation value is less than a thresholdvalue, while “large” indicates that the correlation value is equal to orgreater than a threshold value.

The transmission mode determination unit 504 uses the pattern matchingresult received from the pattern matching unit 503 (the correlationbetween the signal in the lower 1 MHz band and the signal in the higher1 MHz band illustrated in FIG. 18), and on the basis of thecorrespondence relationships illustrated in FIG. 18, determines thetransmission mode (spectral placement mode) being used in the receivedsignal.

In other words, when the above correlation value is “large”, thetransmission mode determination unit 504 determines that the 1 MHzDuplicate format (1D) is being used, in which the same signal is placedin the higher 1 MHz band and the lower 1 MHz band. Also, when the abovecorrelation value is “small”, the transmission mode determination unit504 determines that the 2 MHz format (2C) is being used, in whichdifferent signals are placed in the higher 1 MHz band and the lower 1MHz band.

As illustrated in FIG. 18, the transmission mode determination unit 504is able to determine the transmission mode while distinguishing betweenthe spectral placement modes 1U or 1L, 1D, and 2C. In other words, thetransmission mode determination unit 504 is able to determine thebandwidth of the received signal, and also whether the mode of areceived signal placed in the 2 MHz band is 1D or 2C.

As above, according to the present embodiment, the determination unit102 c is able to use the correlation of signals in the higher 1 MHz bandand the lower 1 MHz band to accurately detect the transmission mode(placement mode), and improve communication efficiency.

Embodiment 5

In the present embodiment, the operation of the determination unit ofthe wireless communication device 100 (FIG. 3) differs compared toEmbodiments 1 to 4.

FIG. 19 is a block diagram illustrating an internal configuration of adetermination unit 102 d according to the present embodiment.

In the determination unit 102 d illustrated in FIG. 19, a delay unit 601delays the received signal received from the tuner 101 by apredetermined time. For example, the delay unit 601 delays the receivedsignal by a time corresponding to the STF in the 2 MHz (short/long)format (see FIG. 1).

A pattern matching unit 602 conducts a pattern matching process(correlation process) on the received signal received from the tuner 101(no delay) and the received signal received from the delay unit 601(delayed).

For example, as illustrated in FIG. 1, the number of symbols in the STFof the 2 MHz format (10 symbols) is half the number of symbols in theSTF of the 1 MHz format (20 symbols). Consequently, for example, thepattern matching unit 602 computes a correlation value between thepre-delay received signal and the delayed received signal. Thecomputation of the above correlation value is conducted during theperiod from a time point after the predetermined delay time elapsessince the beginning of the pre-delay received signal to the time pointafter the of time corresponding to half the number of symbols in the STFof the 1 MHz format elapses. In other words, the pattern matching unit602 computes the correlation value between the pre-delay received signaland the delayed received signal during the period from the beginning ofthe delayed received signal to the time point after the timecorresponding to half the number of symbols in the STF of the 1 MHzformat elapses.

A transmission mode determination unit 603 uses the pattern matchingresult received from the pattern matching unit 602 to determine thetransmission mode (spectral placement mode) being used in the receivedsignal. Specifically, the transmission mode determination unit 603determines that the 1 MHz format is being used when the correlationvalue resulting from the pattern matching process is high, anddetermines that the 2 MHz format is being used when the correlationvalue is low.

Hereinafter, operation of the transmission mode determination process bythe determination unit 102 d will be described in detail.

FIG. 20 illustrates frames using the 1 MHz or 2 MHz communication bandof 802.11ah, and those frames delayed by a time Tx.

As illustrated in FIG. 20, the time Tx is a time that corresponds to theSTF in the 2 MHz format.

In FIG. 20, T is the time at the beginning of a frame, and the periodfrom time T+Tx to time T+Tx+10×T_(S) will be considered. In other words,the period from the point in time (time T+Tx) that is a time Tx afterthe beginning of the pre-delay received signal (time T) to the time(time T+Tx+10×T_(S)) after the elapsing of a time 10×T_(S) correspondingto half the number of symbols in the STF of the 1 MHz format (or thenumber of symbols in the STF of the 2 MHz format) will be considered.

In the 1 MHz case, the above period of time corresponds to part of theSTF in both the pre-delay received signal and the delayed receivedsignal, and corresponds to a segment in which the same signal isrepeatedly placed in the STF. Consequently, in the pattern matchingprocess that the pattern matching unit 602 conducts on these signal, ahighly correlative result is obtained.

On the other hand, in the 2 MHz case, the above period of timecorresponds to the LTF1 in the pre-delay received signal, andcorresponds to the STF in the delayed received signal. In other words,in the above period of time, the pre-delay received signal and thedelayed received signal are different signals. Consequently, in thepattern matching process that the pattern matching unit 602 conducts onthese signal, a lowly correlative result is obtained.

Subsequently, the transmission mode determination unit 603 uses theresult of the pattern matching process (the correlation) from thepattern matching unit 602 to determine the transmission mode being usedin the received signal. In other words, the transmission modedetermination unit 603 determines that the transmission mode is the 1MHz format when the pattern matching process returns a highlycorrelative result, and determines that the transmission mode is the 2MHz format when the pattern matching process returns a lowly correlativeresult.

In this way, in the present embodiment, by varying the value of the timeTx according to the STS period T_(S), the LTS period T_(L), and thedifference between the number of STS and LTS repetitions in the 1 MHz/2MHz formats, the pattern matching results may be differentiated betweenthe 1 MHz format and the 2 MHz format. In so doing, the determinationunit 102 d is able to accurately detect the transmission mode andimprove communication efficiency, on the basis of changes in thecorrelation result from pattern matching.

Note that the present embodiment describes the case of setting the delaytime Tx to a time corresponding to the STF symbols in the 2 MHz format.However, the delay time is not limited thereto, and may be set to anytime insofar as the pattern matching results differ between the 1 MHzformat and the 2 MHz format.

Embodiment 6

FIG. 21 is a block diagram illustrating a configuration of a wirelesscommunication device 700 according to the present embodiment. Note thatin FIG. 21, the same signs are given to components that conduct the sameoperations as Embodiment 1 (FIG. 3), and description thereof will bereduced or omitted.

In the wireless communication device 700 illustrated in FIG. 21, adetermination unit 701 uses the signal received from the FFT unit 104 todetermine the transmission mode being used in the received signal.Specifically, the determination unit 701 determines the transmissionformat being used in the received signal from among multipletransmission formats by using multiple symbols, including the symbolsconstituting the LTF (LTS) and the symbols constituting the SIG from areceived signal using any one of multiple transmission formats thatinclude the LTF and the SIG, and use the lower 1 MHz band or the higher1 MHz band.

FIG. 22 is a block diagram illustrating an internal configuration of thedetermination unit 701. The determination unit 701 includes a symboldifferential computation unit 711, a square computation unit 712, acumulative addition unit 713, and a transmission mode determination unit714.

The symbol differential computation unit 711 conducts a differentialcomputation between the symbols in the LTF or the SIG. The symbolssubjected to the symbol differential computation in the symboldifferential computation unit 711 are the same irrespective of thetransmission format configured in the wireless communication device 700.For example, the symbol differential computation unit 711 conductsdifferential computation between neighboring symbols in the time domainon the three symbols (LTF or SIG) from the 2nd symbol to the 4th symbolstarting from the beginning of the LTF.

The square computation unit 712 conducts a squaring operation on thecomputational result of the symbol differential computation unit 711 ineach subcarrier.

The cumulative addition unit 713 cumulatively adds together thecomputational results from the square computation unit 712 for eachsubcarrier (vector addition).

The transmission mode determination unit 714 determines the transmissionmode being used in the received signal on the basis of the combinationof cumulatively added values (squared results) received from thecumulative addition unit 713. In other words, the transmission modedetermination unit 714 determines the transmission mode being used inthe received signal on the basis of whether the values indicated by thecumulatively added values (squared results) received from the cumulativeaddition unit 713 are positive values or negative values on the realaxis.

[Transmission Mode Determination Method]

FIG. 23 is a diagram illustrating respective frames in transmissionformats of 802.11ah (1 MHz short, 2 MHz short, 2 MHz long), with theframes aligned so that the beginning of the LTF is at time T2. Thewireless communication device 700 detects the timing of the beginning ofthe LTF using the STF, for example.

The symbol differential computation unit 711 extracts the 2nd, 3rd, and4th symbols from the beginning of the LTF (time T2) in the 802.11ahtransmission formats (see FIG. 23), and conducts the symbol differentialcomputation.

FIGS. 24, 25, and 26 are diagrams illustrating four symbols startingfrom the time T2 in the respective frames in the 1 MHz, 2 MHz short, and2 MHz long formats.

As illustrated in FIGS. 24, 25, and 26, the 2nd, 3rd, and 4th symbolsstarting from the beginning of the LTF (time T2) are LTF (LTF) or SIG(SIG1) symbols. Herein, in the LTF, the phase of the pilot for eachsubcarrier is predetermined to be 0 degrees or 180 degrees. In otherwords, the phase of the pilot of the LTF has the same features as themapping of a signal in the BPSK modulation scheme. Meanwhile, SIG (orSIG-A) differ for each transmission format. As illustrated in FIG. 1, inthe 1 MHz format (short and Duplicate), BPSK modulation is used on allsix symbols. On the other hand, in the 2 MHz short format, quadratureBPSK (QBPSK) modulation is used on all two symbols. QBPSK modulation isa scheme in which symbols are phase-modulated at 90 degrees and 270degrees. In other words, the phase differs by 90 degrees from BPSKmodulation. Also, in the 2 MHz long format, QBPSK modulation is used forthe first of two symbols, while BPSK modulation is used for the secondsymbol.

In other words, multiplexed into the SIG are control signals that havebeen modulated according to a modulation scheme (BPSK or QBPSK) thatuses the same phase as, or a phase existing in an orthogonalrelationship with, the phase in which the pilot signal is placed in theLTF.

Hereinafter, operation of the determination unit 701 in the case ofreceiving a signal in each transmission format will be described.

Specifically, in the 1 MHz signal illustrated in FIG. 24, starting froma time T3 after the elapsing of an amount of time T_(Y) since a time T2,the three symbols LTS2, LTS3, and LTS4 are placed consecutively in thetime domain. The symbol differential computation unit 711 computes thesymbol differential between neighboring symbols in the time domain onthese three symbols. All of these LTS are modulated using BPSK, in whichsignal points are mapped onto the real axis of the complex plane. Thus,as illustrated in FIG. 24, the result of the symbol differential betweenLTS2 and LTS3 as well as the result of the symbol differential betweenLTS3 and LTS4 are both positive values on the real axis of the complexplane. Subsequently, the square computation unit 712 computes the squareof the symbol differential results. As illustrated in FIG. 24, thesquare of the symbol differential between LTS2 and LTS3 as well as thesquare of the symbol differential between LTS3 and LTS4 are bothpositive values on the real axis of the complex plane.

In the 2 MHz short signal illustrated in FIG. 25, starting from the timeT3 after the elapsing of the amount of time T_(Y) since the time T2, thethree symbols LTS2, SIG1, and SIG2 are placed consecutively in the timedomain. The symbol differential computation unit 711 computes the symboldifferential between neighboring symbols in the time domain on thesethree symbols. As discussed above, the LTS is modulated using BPSK, inwhich signal points are mapped onto the real axis of the complex plane.Meanwhile, the SIG symbols are modulated using QBPSK, in which signalpoints are mapped onto the imaginary axis of the complex plane. Thus, asillustrated in FIG. 25, the result of the symbol differential betweenLTS2 and SIG1 is a value on the imaginary axis of the complex plane.Also, the result of the symbol differential between SIG1 and SIG2 is avalue on the real axis of the complex plane. Subsequently, the squarecomputation unit 712 computes the square of the symbol differentialresults. As illustrated in FIG. 25, the square of the symboldifferential between LTS2 and SIG1 is a negative value on the real axisof the complex plane. Also, the square of the symbol differentialbetween SIG1 and SIG2 is a positive value on the real axis of thecomplex plane.

In the 2 MHz long signal illustrated in FIG. 26, starting from the timeT3 after the elapsing of the amount of time T_(Y) since the time T2, thethree symbols LTS2, SIGA1, and SIGA2 are placed consecutively in thetime domain. The symbol differential computation unit 711 computes thesymbol differential between neighboring symbols in the time domain onthese three symbols. As discussed above, the LTS is modulated usingBPSK, in which signal points are mapped onto the real axis of thecomplex plane. Meanwhile, SIGA1 is modulated using QBPSK, in whichsignal points are mapped onto the imaginary axis of the complex plane,and SIGA2 is modulated using BPSK. Thus, as illustrated in FIG. 26, theresult of the symbol differential between LTS2 and SIGA1 as well as theresult of the symbol differential between SIGA1 and SIGA2 are bothvalues on the imaginary axis of the complex plane. Subsequently, thesquare computation unit 712 computes the square of the symboldifferential results. As illustrated in FIG. 26, the square of thesymbol differential between LTS2 and SIGA1 as well as the square of thesymbol differential between SIGA1 and SIGA2 are both negative values onthe real axis of the complex plane.

In other words, the combination of modulation schemes used for the threesymbols after time T3 differs according to the transmission format.Consequently, the results of the symbol differential computation and thesquare computation on the three symbols after time T3 differ accordingto each transmission format. For this reason, the transmission modedetermination unit 714 determines the transmission mode on the basis ofthe results of the symbol differential computation and the squarecomputation.

Specifically, when the squared result of the second and third symbolsstarting from the beginning of the LTF and the squared result of thethird and fourth symbols starting from the beginning of the LTF are bothpositive values on the real axis (FIG. 24), the transmission modedetermination unit 714 determines that the 1 MHz format is being used,in which all SIG control signals are modulated by a modulation scheme(BPSK) that uses phases existing in an in-phase relationship with thephase of the LTF pilot signal.

Also, when the squared result of the second and third symbols startingfrom the beginning of the LTF is a negative value on the real axis, andthe squared result of the third and fourth symbols starting from thebeginning of the LTF is a positive value on the real axis, thetransmission mode determination unit 714 determines that the 2 MHz shortformat is being used, in which all SIG control signals are modulated bya modulation scheme (QBPSK) that uses a phase existing in an orthogonalrelationship with the phase of the LTF pilot signal.

Also, when the squared result of the second and third symbols startingfrom the beginning of the LTF and the squared result of the third andfourth symbols starting from the beginning of the LTF are both negativevalues on the real axis, the transmission mode determination unit 714determines that the 2 MHz long format is being used, in which one SIGcontrol signal is modulated by a modulation scheme (QBPSK) that usesphases existing in an orthogonal relationship with the phase of the LTFpilot signal, while the other control signal is modulated by amodulation scheme (BPSK) that uses phases existing in an in-phaserelationship with the phase of the LTF pilot signal.

Also, the cumulative addition unit 713 cumulatively adds over allsubcarriers the values of the squared result obtained by the operationson each subcarrier illustrated in FIGS. 24 to 26. In so doing, thecomputational results obtained for each subcarrier may be averaged,enabling the transmission mode determination unit 714 to accuratelydetermine whether the computational results are mapped to the real axisor the imaginary axis.

FIGS. 27 and 28 are flowcharts illustrating a process flow of thetransmission mode determination method discussed above. Specifically,FIG. 27 illustrates a process of determining three types of transmissionmodes (1 MHz, 2 MHz short, and 2 MHz long), while FIG. 28 illustrates aprocess of determining 1L, 1U, and 1D from among the 1 MHz transmissionmodes.

In FIGS. 27 and 28, the following parameters are used.

A-diff1: the result of squaring the symbol differential between thefirst and second symbols since time T3

A-diff2: the result of squaring the symbol differential between thesecond and third symbols since time T3

AL-diff1: the value corresponding to the lower 1 MHz band of A-diff1

AU-diff1: the value corresponding to the higher 1 MHz band of A-diff1

AL-diff2: the value corresponding to the lower 1 MHz band of A-diff2

AU-diff2: the value corresponding to the higher 1 MHz band of A-diff2

In FIG. 27, in ST101, the transmission mode determination unit 714determines whether or not the real part of the complex number A-diff1 isless than 0. When the real part of the complex number A-diff1 is notless than 0 (ST101: No), in ST102, the transmission mode determinationunit 714 determines that the transmission mode of the received signal isthe 1 MHz format.

When the real part of the complex number A-diff1 is less than 0 (ST101:Yes), in ST103, the transmission mode determination unit 714 determineswhether or not the real part of the complex number A-diff2 is less than0. When the real part of the complex number A-diff2 is not less than 0(ST103: No), in ST104, the transmission mode determination unit 714determines that the transmission mode of the received signal is the 2MHz short format.

On the other hand, when the real part of the complex number A-diff2 isless than 0 (ST103: Yes), in ST105, the transmission mode determinationunit 714 determines that the transmission mode of the received signal isthe 2 MHz long format.

Also, in FIG. 28, in ST201, the transmission mode determination unit 714determines whether or not the real part of the complex number AU-diff1is at least 0 with an amplitude that is at least a threshold value, andin addition, the real part of the complex number AL-diff1 is at least 0with an amplitude that is at least a threshold value.

When the determination condition in ST201 is satisfied (ST201: Yes), inST202, the transmission mode determination unit 714 determines thetransmission mode of the received signal to be the 1 MHz Duplicateformat (1D).

On the other hand, when the determination condition in ST201 is notsatisfied (ST201: No), in ST203, the transmission mode determinationunit 714 determines whether or not the real part of the complex numberAU-diff1 is at least 0, and in addition, the value of AU-diff1 isgreater than the value of AL-diff1.

When the determination condition in ST203 is satisfied (ST203: Yes), inST204, the transmission mode determination unit 714 determines thetransmission mode of the received signal to be 1 MHz 1U.

On the other hand, when the determination condition in ST203 is notsatisfied (ST203: No), in ST205, the transmission mode determinationunit 714 determines whether or not the real part of the complex numberAL-diff1 is at least 0, and in addition, the value of AL-diff1 isgreater than the value of AU-diff1.

When the determination condition in ST205 is satisfied (ST205: Yes), inST206, the transmission mode determination unit 714 determines thetransmission mode of the received signal to be 1 MHz 1L.

On the other hand, when the determination condition in ST205 is notsatisfied (ST205: No), the transmission mode determination unit 714 endsthe process without determining the transmission mode.

In this way, the present embodiment focuses on the differentcombinations of modulation schemes according to transmission format forthe three symbols of the 2nd, 3rd, and 4th symbols starting from thebeginning of the LTF, and the wireless communication device 700determines the transmission mode on the basis of the differentials ofthe modulation schemes of symbols including the LTF and the SIG. In sodoing, the transmission mode may be accurately detected, andcommunication efficiency may be improved.

Note that in the present embodiment, the transmission mode is determinedaccording to whether an I-axis signal obtained by a squaring operationis positive or negative. However, since the magnitude of the signaldistribution on the I axis and the Q axis differs by transmission modebefore the squaring operation, obviously it is also possible todetermine the transmission mode by using a magnitude comparison betweenthe total magnitude of the I-axis signal and the total magnitude of theQ-axis signal.

Embodiment 7

In the present embodiment, the operation of the determination unit inFIG. 21 differs compared to Embodiment 6. FIG. 29 is a block diagramillustrating an internal configuration of a determination unit 701 aaccording to the present embodiment. The determination unit 701 aincludes a 1 MHz 1L channel estimation unit 720, a 1 MHz 1U channelestimation unit 730, a 2 MHz channel estimation unit 740, powercalculation units 725, 735, and 745, and a transmission modedetermination unit 750.

A frequency-domain OFDM signal (received signal) output from the FFTunit 104 is input into the determination unit 701 a, and thefrequency-domain OFDM signal is supplied to the 1 MHz 1L channelestimation unit 720, the 1 MHz 1U channel estimation unit 730, and the 2MHz channel estimation unit 740.

When a 1 MHz 1L signal is input, the 1 MHz 1L channel estimation unit720 outputs an estimated channel state value. On the other hand, when asignal other than 1 MHz 1L is input, the 1 MHz 1L channel estimationunit 720 outputs energy-diffuse noise.

When a 1 MHz 1U signal is input, the 1 MHz 1U channel estimation unit730 outputs an estimated channel state value. On the other hand, when asignal other than 1 MHz 1U is input, the 1 MHz 1U channel estimationunit 730 outputs energy-diffuse noise.

When a 2 MHz (2C) signal is input, the 2 MHz channel estimation unit 740outputs an estimated channel state value. On the other hand, when asignal other than 2 MHz (2C) is input, the 2 MHz channel estimation unit740 outputs energy-diffuse noise.

The power calculation unit 725 calculates the power of the output fromthe 1 MHz 1L channel estimation unit 720, while the power calculationunit 735 calculates the power of the output from the 1 MHz 1U channelestimation unit 730, and the power calculation unit 745 calculates thepower of the output from the 2 MHz channel estimation unit 740. Eachcalculated power is respectively supplied to the transmission modedetermination unit 750.

The transmission mode determination unit 750, on the basis of each powerreceived from the power calculation units 725, 735, and 745, determinesand outputs whether the transmission mode being used in the receivedsignal is 1 MHz 1L, 1 MHz 1U, 1 MHz 1D, or 2 MHz (2C).

[Transmission Mode Determination Method]

In the present embodiment, similarly to Embodiment 6, the wirelesscommunication device 700 detects the timing of the beginning of the LTFusing the STF as illustrated in FIG. 23, for example.

The 2 MHz short LTF1 and the 2 MHz long LTF1 are the same signal, butthe 2 MHz and 1 MHz LTF1 each has a characteristic, predetermined phasepattern of the pilot multiplexed into each subcarrier in the frequencydomain, so that the 2 MHz and the 1 MHz LTF1 are mutually orthogonal. Inother words, the 2 MHz and 1 MHz LTF1 are different pilot phasepatterns.

Consequently, for an LTS signal in 2 MHz format of a frequency-domainOFDM signal, the channel of the carrier position where the pilot signalis multiplexed may be estimated through complex division by the 2 MHzLTS pilot phase predetermined for each subcarrier. Spectrally, thisestimated channel state value forms a line spectrum with concentratedenergy.

On the other hand, when the LTS signal in 2 MHz format of afrequency-domain OFDM signal is complexly divided by the 1 MHz LTS pilotphase predetermined for each subcarrier, since the 2 MHz and 1 MHz LTSare mutually orthogonal (uncorrelated), energy is diffused in the band,and the spectrum becomes noise uniformly distributed in the band.

The total energy of the former line spectrum with concentrated energyand the total energy of the latter noise uniformly distributed in theband are equal, but the distribution conditions differ. At this point,by conducting the filtering process of the band limiting that allows therange containing the channel spectrum to pass through, the energy of theformer after passing through the filter is unchanged, but the energy ofthe latter decreases after passing through the filter, with the decreasein energy being proportional to the narrowness of the passband width.

In other words, the determination unit 701 a conducts channel estimationusing the LTS pilot phase pattern of each format, respectively computesthe power of the estimated channel state value after going through aband limit filter, and determines that the transmission format beingused in the received signal is the transmission format that correspondsto largest calculated power calculated from among the powers of theestimated channel state values for each format.

Specifically, the 1 MHz 1L channel estimation unit 720 includes a 1 MHz1L pilot pattern generator 721, a complex division unit 722, a symbolfilter 723, and a carrier filter 724.

The 1 MHz 1L pilot pattern generator 721 generates a known phase patternof the 1 MHz 1L pilot signal at the same timings as the subcarriers intowhich are inserted the pilot signals of the 1st and 2nd symbols in theLTF1 of the frequency-domain OFDM signal, and outputs the generatedphase pattern to the complex division unit 722.

The complex division unit 722 assumes that the frequency-domain OFDMsignal is in the 1 MHz 1L format, and from the frequency-domain OFDMsignal extracts the signal of the subcarrier positions where the pilotsignals of the 1st and 2nd symbols in the LTF1 of the 1 MHz 1L formatare multiplexed. Subsequently, the complex division unit 722 conductschannel estimation by complexly dividing the extracted subcarrier signalby the known phase pattern generated from the 1 MHz 1L pilot patterngenerator 721 corresponding to that carrier placement, and outputs anestimated channel state value to the symbol filter 723.

The symbol filter 723 accepts the estimated channel state value from thecomplex division unit 722 as input, conducts a filtering process in thesymbol direction, and outputs to the carrier filter 724. For example,the symbol filter 723 uses the estimated channel state value of the 1stsymbol and the 2nd symbol in the LTF1 to output the average between thetwo symbols in each subcarrier.

The carrier filter 724 accepts the estimated channel state value outputby the symbol filter 723 as input, conducts a filtering process in thecarrier direction, and outputs to the power calculation unit 725. Forexample, the carrier filter 724 may be a filter with time-amplitudecharacteristics that sets the guard interval length of the OFDM signalas the passband.

The 1 MHz 1U channel estimation unit 730 includes a 1 MHz 1U pilotpattern generator 731, a complex division unit 732, a symbol filter 733,and a carrier filter 734.

The 1 MHz 1U pilot pattern generator 731 generates a known phase patternof the 1 MHz 1U pilot signal at the same timings as the subcarriers intowhich are inserted the pilot signals of the 1st and 2nd symbols in theLTF1 of the frequency-domain OFDM signal, and outputs the generatedphase pattern to the complex division unit 732.

The complex division unit 732 assumes that the frequency-domain OFDMsignal is in the 1 MHz 1U format, and from the frequency-domain OFDMsignal extracts the signal of the subcarrier positions where the pilotsignals of the 1st and 2nd symbols in the LTF1 of the 1 MHz 1U formatare multiplexed. Subsequently, the complex division unit 732 conductschannel estimation by complexly dividing the extracted subcarrier signalby the known phase pattern generated from the 1 MHz 1U pilot patterngenerator 731 corresponding to that carrier placement, and outputs anestimated channel state value to the symbol filter 733.

The symbol filter 733 and the carrier filter 734 conduct filteringprocesses that limit the estimated channel state value to the passband,and output to the power calculation unit 735. Since the symbol filter733 is a filter having the same characteristics and function as thesymbol filter 723 described earlier, further description will beomitted. Also, since the carrier filter 734 is a filter having the samecharacteristics and function as the carrier filter 724 describedearlier, further description will be omitted.

The 2 MHz channel estimation unit 740 includes a 2 MHz pilot patterngenerator 741, a complex division unit 742, a symbol filter 743, and acarrier filter 744.

The 2 MHz pilot pattern generator 741 generates a known phase pattern ofthe 2 MHz pilot signal at the same timings as the subcarriers into whichare inserted the pilot signals of the 1st and 2nd symbols in the LTF1 ofthe frequency-domain OFDM signal, and outputs the generated phasepattern to the complex division unit 742.

The complex division unit 742 assumes that the frequency-domain OFDMsignal is in the 2 MHz format, and from the frequency-domain OFDM signalextracts the signal of the subcarrier positions where the pilot signalsof the 1st and 2nd symbols in the LTF1 of the 2 MHz format aremultiplexed. Subsequently, the complex division unit 742 conductschannel estimation by complexly dividing the extracted subcarrier signalby the known phase pattern generated from the 2 MHz pilot patterngenerator 741 corresponding to that carrier placement, and outputs anestimated channel state value to the symbol filter 743.

The symbol filter 743 and the carrier filter 744 conduct filteringprocesses that limit the estimated channel state value to the passband,and output to the power calculation unit 745. Since the symbol filter743 is a filter having the same characteristics and function as thesymbol filter 723 described earlier, further description will beomitted. Also, since the carrier filter 744 is a filter having the samecharacteristics and function as the carrier filter 724 describedearlier, further description will be omitted.

The transmission mode determination unit 750 takes the output of thepower calculation unit 725 to be the 1 MHz 1L power value, the output ofthe power calculation unit 735 to be the 1 MHz 1U power value, theoutput of the power calculation unit 745 to be the 2 MHz power value,and the sum of the output of the power calculation unit 725 and theoutput of the power calculation unit 735 to be the 1 MHz 1D. Thetransmission mode determination unit 750 then makes a weighted magnitudecomparison of the respective power values, and outputs the format of thepower value exhibiting the greatest value as the transmission mode beingused in the received signal.

For example, the transmission mode determination unit 750 compares the 2MHz power value, the 1 MHz 1L power value, and the 1 MHz 1U power value,and when the 2 MHz power value is the greatest, determines that the 2MHz format is the transmission format being used in the received signal.Otherwise, the transmission mode determination unit 750 compares thepower value of the 1 MHz 1L and the power value of the 1 MHz 1U weightedby a weighting coefficient α to the 1 MHz 1D power value. When the 1 MHz1D power value is the greatest, the transmission mode determination unit750 determines that the 1 MHz 1D format is the transmission format beingused in the received signal. Otherwise, the transmission modedetermination unit 750 compares the 1 MHz 1L power value and the 1 MHz1U power value, and determines the greater value to be the transmissionformat being used in the received signal.

In this way, according to the present embodiment, by focusing ondifferences in the pilot phase pattern in the 1st and 2nd symbolsstarting from the beginning of the LTF1, the wireless communicationdevice 700 determines the transmission mode on the basis of the power ofthe estimated channel state value calculated using the pilot pattern ofeach transmission mode (transmission format) and the received signal(frequency-domain OFDM signal). In so doing, the transmission mode maybe accurately detected, and communication efficiency may be improved.

Embodiment 8

In the present embodiment, the transmission mode determination unit 202of the wireless communication device 100 in Embodiment 1 (FIG. 5) orEmbodiment 2 (FIG. 7) determines the transmission mode using differencesin the number of peaks in the correlation obtained as a result ofpattern matching, or alternatively, in the time period during which thepeaks periodically appear.

For example, as illustrated in FIG. 30A, in the case of the 1 MHztransmission format, 20 STS are placed in the STF. Thus, as illustratedin FIG. 30A, there are 20 peaks in the correlation obtained as a resultof pattern matching with a pattern internally held in the receiver(wireless communication device 100), and the time period during whichthe peaks periodically appear is T_(S)×20.

Meanwhile, as illustrated in FIG. 30B, in the case of the 2 MHztransmission format, 10 STS are placed in the STF. Thus, as illustratedin FIG. 30B, there are 10 peaks in the correlation obtained as a resultof pattern matching with a pattern internally held in the receiver(wireless communication device 100), and the time period during whichthe peaks periodically appear is T_(S)×10.

Similarly, in the LTF, differences occur between 1 MHz and 2 MHz in thenumber of peaks in the correlation as well as the time period duringwhich the peaks periodically appear.

Accordingly, in the present embodiment, the transmission modedetermination unit 202 (FIG. 5 or 7) determines the transmission formatused in the received signal on the basis of the number of peaks in thepattern matching result (correlation) received from the pattern matchingunits 201-1 to 201-4, or alternatively, the time period during which thepeaks in the above correlation periodically appear.

For example, when there are 20 (or approximately 20) peaks in the abovecorrelation, or when the time period during which the peaks in thecorrelation periodically appear is T_(S)×20 (or approximately T_(S)×20),the transmission mode determination unit 202 determines that the 1 MHzformat is being used in the received signal. Similarly, when there are(or approximately 10) peaks in the above correlation, or when the timeperiod during which the peaks in the correlation periodically appear isT_(S)×10 (or approximately T_(S)×10), the transmission modedetermination unit 202 determines that the 2 MHz format is being used inthe received signal.

In this way, according to the present embodiment, by focusing ondifferences in the number of symbols in the STF or the LTF for eachtransmission format, the wireless communication device 100 determinesthe transmission mode on the basis of the received signal, and thenumber of peaks in the result of a pattern matching process (thecorrelation) with a stored preamble pattern, or the time period duringwhich the peaks periodically appear. In so doing, the transmission modemay be accurately detected, and communication efficiency may beimproved.

The foregoing thus describes exemplary embodiments of the presentdisclosure.

Note that the transmission mode determination methods described in theexemplary embodiments may also be combined. For example, thetransmission mode determination method of Embodiment 3 and thetransmission mode determination method of Embodiment 4 may be combined.

Also, the structural elements (function blocks) of the wirelesscommunication device described in the foregoing exemplary embodimentsmay be realized as an integrated circuit via LSI. In this case, therespective structural elements may be realized individually as separatechips, or as a single chip that includes some or all structuralelements. Also, although LSI is discussed herein, the circuitintegration methodology may also be referred to as IC, system LSI, superLSI, or ultra LSI, depending on the degree of integration.

Furthermore, the circuit integration methodology is not limited to LSI,and may be also be realized with special-purpose circuits orgeneral-purpose processors. A field-programmable gate array (FPGA)capable of being programmed after fabrication, or a reconfigurableprocessor whose circuit cell connections and settings may bereconfigured, may also be used.

Furthermore, when circuit integration technology that may be substitutedfor LSI appears as a result of progress in semiconductor technology oranother derived technology, obviously the new technology may be used tointegrate the function blocks. Biotechnology applications and the likeare also a possibility.

In addition, the wireless communication device and wirelesscommunication method indicated in the foregoing exemplary embodimentsmay also be realized using a method that conducts at least part of theprocesses described herein.

Also, at least part of the operating procedures of the wirelesscommunication device indicated in the foregoing exemplary embodimentsmay be stated in a program, and a central processing unit (CPU) may readout and execute such a program stored in memory, or the program may besaved to a recording medium and distributed or the like, for example.

Also, the foregoing exemplary embodiments may also be realized bycombining any devices, method, circuit, or programs that conduct part ofthe processes that realize the foregoing exemplary embodiments. Forexample, part of the configuration of the wireless communication devicedescribed in the foregoing exemplary embodiments may be realized with awireless communication device or integrated circuit, while the operatingprocedures conducted by the configuration other than that part may bestated in a program, and the foregoing exemplary embodiments may berealized as a result a CPU reading out and executing the program storedin memory, for example.

The present disclosure is useful for a communication system thatselectively uses multiple transmission modes having differences in thepreamble and signal placement, such as IEEE 802.11ah.

What is claimed is:
 1. A wireless communication device comprising: areceiving unit that receives a signal using one of a plurality oftransmission formats that use at least one of a first frequency band anda second frequency band; and a determination unit that determines atransmission format being used in the received signal from among theplurality of transmission formats, the determination unit comprising apattern matching unit that stores a plurality of patterns respectivelyexpressing a received waveform of a preamble in each of the plurality oftransmission formats, conducts a pattern matching between the receivedsignal and each of the plurality of patterns, and obtains a correlationvalue, and a mode determination unit that determines the transmissionformat being used in the received signal based on the obtainedcorrelation value.
 2. The radio communication device according to claim1, wherein the determination unit further comprises: a first extractionunit that extracts a first component of the first frequency band fromthe received signal; and a second extraction unit that extracts a secondcomponent of the second frequency band from the received signal; andwherein the pattern matching unit obtains the correlation value byconducting a first pattern matching between the first component of thereceived signal and a pattern corresponding to a transmission formatthat uses the first frequency band, conducting a second pattern matchingbetween the second component of the received signal and a patterncorresponding to a transmission format that uses the second frequencyband, and conducting a third pattern matching between the receivedsignal and a pattern corresponding to a transmission that uses the firstfrequency band and the second frequency band.
 3. The wirelesscommunication device according to claim 1, wherein the modedetermination unit determines a transmission format corresponding to apattern with the highest correlation value as the transmission formatbeing used in the received signal.
 4. The wireless communication deviceaccording to claim 1, wherein the mode determination unit determines thetransmission format being used in the received signal based on a numberof peaks in the correlation value, or a time period during which peaksof the correlation value periodically appear.
 5. A wirelesscommunication method comprising: receiving a signal using one of aplurality of transmission formats that use at least one of a firstfrequency band and a second frequency band; and determining atransmission format being used in the received signal from among theplurality of transmission formats; wherein the determining of thetransmission format comprises storing a plurality of patternsrespectively expressing a received waveform of a preamble in each of theplurality of transmission formats, conducting a pattern matching betweenthe received signal and each of the plurality of patterns, and obtaininga correlation value, and determining the transmission format being usedin the received signal based on the correlation value.
 6. A wirelesscommunication method according to claim 5, wherein the determining ofthe transmission format further comprises: extracting a first componentof the first frequency band from the received signal; and extracting asecond component of the second frequency band from the received signal,and wherein the correlation value is obtained by conducting a firstpattern matching process between the first component of the receivedsignal and a pattern corresponding to a transmission format that usesthe first frequency band, conducting a second pattern matching processbetween the second component of the received signal and a patterncorresponding to a transmission format that uses the second frequencyband, and conducting a third pattern matching process between thereceived signal and the pattern corresponding to a transmission thatuses the first frequency band and the second frequency band.
 7. Awireless communication method according to claim 5, wherein thedetermining of the transmission format further comprises: extracting afirst component of the first frequency band from the received signal;shifting the frequency of the first component toward higher frequency byhalf the width of the first frequency band; extracting a secondcomponent of the second frequency band from the received signal; andshifting the frequency of the second component toward lower frequency byhalf the width of the second frequency band, wherein the correlationvalue is obtained by conducting a pattern matching between thefrequency-shifted first component and the frequency-shifted secondcomponent.